A phenomenon that is often present in an electrically operated needle valve is the needle valve bouncing that occurs when the needle valve closes on a seat. Where the needle valve is part of a solenoid operated fuel injector, the occurrence of such bouncing will typically result in an extra amount of unscheduled fuel being injected from the fuel injector into the engine, and this extra fuel can have an adverse effect on fuel economy and engine exhaust constituents. It is therefore desirable to eliminate such bouncing.
Various means for eliminating such bouncing have been proposed, including those found in commonly assigned U.S. Pat. Nos. 4,878,650; 5,033,176; and 5,139,224.
The present invention relates to an impact dampened armature and needle valve assembly wherein a very small amount of axial lost motion is provided between the armature and the needle valve so that when the needle valve impacts the valve seat at closing, the armature motion toward the seat is not immediately arrested, but rather will continue until it impacts a flange of the needle valve. By use of known computational and/or empirical techniques, the timing of the armature's impact with the needle valve flange can be set to occur just as the needle valve begins to bounce from the seat such that the armature substantially reduces or even fully cancels out the bounce.
An advantage of the invention is that no additional impact damping mechanism need be added to the needle valve and armature. All that is required is to axially capture the armature on the needle valve so that a small amount of axial lost motion travel of the former relative to the latter is present. The amount of such lost motion is quite small in the case of a fuel injector, and a dimension of the order of tens of millionths of an inch is typical. The attainment of such dimensions is possible with modern manufacturing techniques and materials.
The foregoing features, advantages, and benefits of the invention will be seen in the ensuing description and claims which are accompanied by a drawing. The drawing and description disclose a presently preferred embodiment of the invention according to the best mode contemplated at the present time for carrying out the invention.